| 摘要 |
The invention relates to finely divided polyvinyl acetal which is prepared in the form of an aqueous suspension or, if desired, in powder form, preferably having average particle sizes from 0.5 to 10 mu m, from polyvinyl alcohol and at least one aliphatic aldehyde having at least 3 carbon atoms, and which contains 0.1 to 10% by weight, based on polyvinyl acetal, of a completely or partially hydrolyzed vinyl ester copolymer grafted onto polyethylene oxide or polyethylene oxide derivatives and acetalized in the mixture with the polyvinyl alcohol. The invention further relates to a process for preparing finely divided polyvinyl acetals having an average particle size between 0.5 and 10 mu m in an aqueous suspension or, if desired, by dewatering the suspension, in powder form, by reacting an aqueous solution of polyvinyl alcohol, in the presence of an acidic catalyst and in the absence or presence of emulsifiers, with at least one aliphatic aldehyde having at least 3 carbon atoms, which comprises performing the acetalization reaction in the presence of 0.1 to 10% by weight, based on the polyvinyl alcohol used, of a completely or partially hydrolyzed graft copolymer of vinyl ester on polyethylene oxide or polyethylene oxide derivatives. A further part of the subject-matter of the invention is the use of the finely divided polyvinyl acetals described above, in particular from a low-electrolyte or electrolyte-free aqueous suspension, preferably having an average particle size between 0.5 and 10 mu m, for baked coatings on any coatable substrates, in particular on metals. |
